66. The effective resistance R
eff
satisfies I
2
rms
R
eff
= P
mechanical
, or
R
eff
=
P
mechanical
I
2
rms
=
(0.100 hp)(746 W/hp)
(0.650 A)
2
= 177 Ω .
This is not the same as the resistance R of its coils, but just the effective resistance for power transfer
from electrical to mechanical form. In fact I
2
rms
R would not give P
mechanical
but rather the rate of energy
loss due to thermal dissipation.